The present invention relates to a thermally addressable liquid crystal display device, and more particularly to a laser-addressed high-resolution liquid crystal light valve.
Display devices used as the terminal devices of computers are required to have high resolution, due to the large capacities and increased capabilities of modern day large and small frame computers. In such computer applications such as image processing, newspaper composition, LSI design, etc., it is especially important that the display devices have both high resolution and discrete display element addressing. In a conventional cathode ray tube (CRT) such displays have not been realized due to the difficulty of enhancing resolution up to 2000 lines or more for a given display area. Accordingly, other display devices which could potentially produce higher resolution have been investigated. In an article entitled "Laser-Addressed Liquid Crystal Projection Displays" in the technical journal "Proceeding of the S.I.D." Vol. 19, No. 1, First Quarter 1978, p.p. 1-7, A. G. Dewey et al discusses a laser-addressed smectic liquid crystal light valve. Both a dielectric multi-layer film and a reflective electrode film are formed onto a rear glass plate. A front glass plate is provided with a transparent electrode film. Both front and rear glass plates are further provided with alignment films for alignment with respect to one another. A liquid crystal material is sandwiched between the rear and front glass plates. When a laser beam is focused onto the dielectric multi-layer films of the rear glass plate, it is absorbed and converted into heat. The heat is transmitted through both the reflective electrode film and the alignment film of the rear glass plate, raising the temperature of the liquid crystal material. A smectic liquid crystal is used as the liquid crystal material, such that as the temperature rises, the liquid crystal undergoes a nematic to liquid phase change. When the laser beam is subsequently removed, this phase change results in the random alignment of liquid crystal molecules in a frozen scattering mode. The scattering mode is "read out" by a light projected from the side of the front glass plate, and displayed on a screen.
According to this display technique, a line width of 10 .mu.m can be generated, such that over 5000 lines of information can be recorded in a single liquid crystal light valve of two inches square. Thus, it is possible to realize a display which has a high resolution as compared to the conventional CRT display devices of the prior art.
Since the liquid crystal light valve operates to record information by converting laser light into heat, the speed and the contrast of the liquid crystal display are closely related to the light adsorption characteristic of the dielectric multi-layer films. To accurately form the dielectric multi-layer films, it is necessary to vapor-deposit onto the rear glass plate inorganic materials having high refractive indices (such as zinc sulfide (ZnS), arsenic sulfide (As.sub.2 S.sub.3), etc. However, in such a multi-layer structure, gaps between layers occurs where the lattice constants of the respective layers have not been accurately matched. This serves to adversely affect the overall reliability of the display device.